1. Field of the Invention
The present invention relates to a power source for an ultrasonically driven surgical handpiece.
2. Background Information
The lens of a human eye may develop a cataracteous condition which affects a patients vision. Cataracteous lenses are sometimes removed and replaced in a procedure commonly referred to as phacoemulsification. Phaco procedures are typically performed with an ultrasonically driven handpiece which is used to break the lens. The broken lens is removed through an aspiration line that is coupled to the handpiece. The aspiration line is connected to a pump which creates a vacuum pressure within the line.
The handpiece has a tip which is inserted through an incision in the cornea. The handpiece typically contains a number of ultrasonic transducers which convert electrical power into a mechanical oscillating movement of the tip. The distal end of the tip has an opening which is in fluid communication with the aspiration line. The oscillating movement of the tip breaks the lens into small pieces that are then drawn into the aspiration line through the tip opening.
The handpiece is connected to a console that contains a power source which drives the ultrasonic transducers. The power provided to the transducers can be controlled by the surgeon through a foot pedal that is connected to the console. During a phaco procedure a piece of the broken lens may be too large to be drawn through the tip. Such a condition may create an occlusion at the tip opening. The surgeon can further break up the piece by depressing the foot pedal and increasing the power to the transducers.
The tip occlusion reduces the vacuum pressure within the aspiration line downstream from the cornea. When the occlusion is removed there is a sudden change in pressure within the cornea. The sudden change in pressure may collapse the cornea. The surgeon must perform the procedure with skill to insure that this event does not occur.
U.S. Pat. No. 5,591,127 issued to Barwick Jr. et al. discloses a phaco system that senses the vacuum pressure within the aspiration line and varies the speed of the pump when the line pressure falls below a threshold vacuum level. The reduction in pump speed lowers the rate at which the vacuum pressure decreases while the aspiration line is occluded. Because of mechanical and pneumatic inertia, there is typically a time delay between when the vacuum pressure falls below the threshold value and when the reduced pump speed lowers the vacuum pressure. This time delay may allow an undesirable increase in the vacuum pressure of the aspiration line.
U.S. Pat. No. 4,395,258 issued to Wang et al. discloses an aspiration system that contains a pair of electronically controlled valves to control the vacuum pressure within an aspiration line. One of the valves controls the flow between the aspiration line and a vacuum pump. The other valve controls the flow of air from the atmosphere into the aspiration line. The valves are switched between open and closed positions by a controller that receives a feedback signal from a pressure transducer. The pressure transducer senses the vacuum pressure within the aspiration line.
The controller receives an input signal from a foot pedal that can be depressed by the surgeon. The controller compares the feedback signal from the pressure transducer with the input signal from the foot pedal. The controller can open and/or close either control valve based on the comparision between the two input signals. When used with an ultrasonically driven handpiece the Wang system requires two foot pedals. One foot pedal for the handpiece and another foot pedal for the aspiration system. It would be desirable to provide an ultrasonically driven handpiece/aspiration system that has only one foot pedal and automatically controls the vacuum pressure of the aspiration line.
The pressure transducer is typically in fluid communication with the aspiration line. After each procedure the transducer must be disconnected from the aspiration line and sterilized. Such a procedure takes time. Additionally, the sterilization process may degrade the pressure sensor. It would be desirable to provide a non-invasive pressure transducer assembly for an aspiration system.
One embodiment of the present invention is an aspiration system that may include a control valve to allow a flow of fluid into an aspiration line and vary a vacuum pressure within the line. The system may include a pressure transducer that is coupled to the aspiration line by a sensor line and a check valve. The check valve prevents a back flow of fluid from the aspiration line to the pressure line. The system may further have a control circuit that is coupled to the pressure transducer and the control valve. The control circuit may control the control valve and regulate the vacuum pressure within the aspiration line. The control circuit may receive an input signal that also controls a medical handpiece.